Cubic aluminum nitride, cubic gallium nitride and cubic indium nitride have a number of outstanding characteristics, including high hardness, high thermal conductivity, excellent high-temperature properties and high chemical resistance. This has led to their use in electronic circuit boards and the like. Because of their wide band gap, moreover, they have drawn attention as materials for short wavelength LEDs and the like. Aluminum nitride, gallium nitride and indium nitride assume the hexagonal wurtzite structure under normal temperature and normal pressure. Although they are also known to assume the cubic structure as a metastable system, cubic nitrides cannot ordinarily be obtained under normal temperature and pressure conditions.
Wurtzite structure aluminum nitride, for instance, transforms to cubic structure under application of a pressure of several tens of GPa or greater (see, for example, Mashimo, Uchino, Nakamura et al.: Yield properties, phase transition, and equation of state of aluminum nitride (AIN) under shock compression up to 150 GPa, Journal of Applied Physics, Vol. 86, No. 12, 1999, pp. 6710-6716).
Cubic nitride can also be epitaxially grown at a temperature of several hundred degrees Celsius or higher by conducting molecular beam epitaxy on a cubic substrate. This method produces only a very thin film of cubic nitride measuring several tens of nm in thickness (see, for example, Critical Thickness for Transformation of Epitaxially Stabilized Cubic AIN in Superlattices, I. W. Kim, Q. Li, L. D. Marks and S. A. Barnett, Applied Physics Letters 78, 7, 892 (2001)).
Transformation of the crystal structure of a Group XIII nitride from hexagonal to cubic by a static pressure application process (using a press or the like) thus requires application of a pressure of several tens of GPa. This method is therefore incapable of forming cubic nitride as a film on a substrate such as glass or metal. Production of cubic nitride by means of a thin film forming method is costly, is limited to particular substrates, and is incapable of producing film to a thickness greater than 0.1 μm. In addition, the properties of cubic nitrides such as cubic aluminum nitride, cubic gallium nitride and cubic indium nitride are not clearly known in detail owing to the difficulty of their production. These nitrides are, however, known to have better symmetry than hexagonal nitrides and to be low in carrier scattering. As such, they are expected, for example, to improve the efficiency of light-emitting devices and the like.
An object of the present invention is to provide a method of transforming the crystal structure of a Group XIII nitride that enables transformation of a Group XIII nitride to cubic crystal structure using a system of simpler configuration than that used for transforming the crystal structure of a Group XIII nitride by a static pressure application process. Another object of the present invention is to provide a Group XIII nitride unobtainable heretofore and a constituent containing a cubic nitride